Flight hazard warning system



March 10, 1953 M SKOLLER FLIGHT HAZARD WARNING SYSTEM Filed sept. 2, 1947 JONFZOU G a HTH J. ||mm\ u: ITSM?.

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J JNVENTOR MARvsN sKoLLER BY M4 y H1 AGENT Patented Mar. 10, 1953 FLIGHT HAZARD WARNING SYSTEM Marvin Skoller, Los Angeles, Calif., assignor to Hughes Tool Company, Houston, Tex., a corporation of Delaware Application September 2, 1947, Serial No. 771,597

8 Claims.

This invention relates to obstacle detection equipment and in particular to a radio-echo apparatus for use on aircraft to provide warning of the near presence of flight hazards.

A major proportion of aircraft mishaps are attributable to a combination of olf-course flight, the presence of flight hazards, and either poor visibility conditions or a lack of alertness on the part of the aircraft pilot. In particular, there has been an alarming increase in the number of aircraft crashes taking place against mountains at distances no more than several hundred feet below their peaks, crashes which appear to be readily avoidable if some advance warning can .be obtained.

v It is therefore an object of the present invention to provide an obstacle detection apparatus for aircraft, which functions under all weather and visibility conditions to give visual and audible warning of the near presence of flight hazards.

Another object is tov provide a Warning apparatus, for aircraft, in which a Warning indicator or alarm is energized when the clearance or separation distance of the aircraft from underlying or advance terrain, or from any obstacle in the general region of the aircraft, decreases to a preset value.

Another object is to provide a warning system, for aircraft, which produces a rst warning indication or alarm when the aircraft enters a hazard zone, and which produces an additional warning indication or alarm when the hazard distance shortens to less than a pre-set value.

Another object is to provide an electronic apparatus functioning to give warning of rapidly rising ground which generally precedes mountainous terrain.

A further object of the present invention is to provide an improved radio pulse-echo apparatus having means to check the apparatus as to operativeness.

Other objects, features and advantages of the invention will appear from the following description taken in connection with the accompanying drawing in which the single figure is a diagram of a preferred embodiment of the invention.

The invention will be described with particular reference to a system of the radio pulse-echo type, in which Search pulses of high frequency energy are generated and radiated into a selected region, resultant echo pulses are received, and the short time intervals between corresponding search and echo pulses are in effect measured and utilized to indicate the separation distances between the apparatus and the reflection producing bodies.

Referring then to the single figure of the drawing, there is shown in circuit and block diagram form a complete radio pulse-echo system embodying the invention. The transmitter portion of this system includes a modulator I0 which forms modulating pulses at a repetition frequency and instants determined by timer l2. Timer I2 may be of blocking oscillator type and designed for operation at say 400 cycles per second. Modulator lll includes a gaseous grid-controlled tube i4. commercially known as a thyratron, which dashes or fires once per cycle of voltage furnished by timer l2, and effectively presents a short circuit between its cathode and plate at such instants. The resultant sharp fall in voltage causes a pulse to be generated by a highly damped tuned circuit comprising capacitor I6, inductance IB and pulse transformer 2|), serially connected in the stated order between the plate and cathode of thyratron I4. The charge built up in capacitor I6 in the period preceding the firing of thyratron I4 is in effect suddenly applied to this tuned circuit, and the resultant pulse generated across the secondary of pulse transformer 2|] is of large amplitude and brief duration, determined by the constants of the tuned circuit. Modulator Ill may, for example, be designed to deliver a pulse of approximately 0.4 micro-second duration. satisfactory for radio-echo purposes and suitably narrow for a short range warning gate as later described.

Ultra-high-frequency oscillator 22 is energized by or modulated in accordance with the modulator pulses, and the corresponding search pulses or bursts of ultra-high-frequency energy are radiated by an antenna 24. The same antenna may also serve for the receiver, as shown, by the use of suitable matching sections 26 and 28 connecting the ultra-high-frequency oscillator 22 and the input stage of the receiver, respectively, to antenna transmission line 30. Any other means for duplexing may be utilized, or, if preferred, separate antennas for the receiver and transmitter may be provided. The antenna system may be designed and mounted to have a broad pattern which covers not only those hazard regions in the immediate flight path of the aircraft but also below and to the sides. The advantage of such a field pattern is that warning of head-on and other hazards are available regardless of the aircraft attitude or course of flight. While here shown schematically as a dipoley the antenna may take any other desired form which provides suiiicient radiation in the stated directions to cover the hazard regions.

Echo pulses, reflected from objects lying within the radiation field of the antenna and picked up by the pulse receiver, are converted to an intermediate frequency signal by a first detector and local oscillator 32, and applied to an intermediate frequency amplifier 34 utilizing screen grid tubes. One or more of these screen grid tubes are maintained in blocked condition eX- cept during `.certain brief intervals. For example, screen grid 36 of intermediate frequency tube 38 may be normally held substantially at ground or cathode potential by returning it to ground through a resistor @il and a normally-closed checker switch 42, as shown. Gate pulses, having the necessary durations and time-positions relative to corresponding search pulses, are applied through a gate pulse transformer it and a capacitor 46 to screen grid 3E. Intermediate frequency tube 38 is thus normally blocked, but momentarily and periodically enabled to pass and amplify echo pulses received during the existence of applied gate pulses. The gate pulse 'for 'short range warning is 'here obtained directly from the modulator circuit a, departing from the conventional practice which necessitates Va 'separate gate forming circuit and its shock excitation ortriggering by timer i2, modulator thyratron lli or any other facility especially provided for Ysuch purpose. In the exemplary embodiment of the present invention, the extremely knarrow'modulating pulse formed by modulator le and appearing Vat the primary or pulse transformer 2li is suitably 'retarded by delay line 48 for utilization 'asa short range gate. For example, where it `is -desired that the warning indicator, later described, shall be energized when 'the aircraft .bearing the equipment Vcomes within 500 feeto an -echo-producing hazard, Va `total time span of substantially one vmicrosecond between initiation ofa search pulse'and completion vof a corresponding gate 'pulse is required. Assuming ideal straight-sided pulses, the modulator and search pulses vshould be just under 0.5 micro-second in ltime-length, `and the vrange gate pulses should "be `delayed by an Vamount slightly lgreater 'than the search pulse time-length, in Yorder to prevent continuouslyenergizing the'indicator due to overlapping of `the search pulse and -the gate pulse. In a practical `case where the search Vand gate pulses are not straight-sided, a `distinct -500 foot warning may still `be provided 'by `making vthe modulation pulse narrower, say substantially '10i-i micro-second-in time-length,andldelaying it sufciently to again provide a -total time :span -.of substantially one micro-second between Vinitiation of a searchpulse-and termination fof acorrespending gate'pulse. Additional Vgate pulses for greater rangesfmaybe'providedin a similar .manner, orvby means of one or morergate-formin'gcircuits `5i! and `associated vdelay Alines 52 .connected -b'etweengate pulse transiormeril :and .the lplate 'ofthyratron T4. cuits arehere shown, utilized :as `later described,

'While but two range gate-.cir-

.it is to be understood .that as :manyrange gates may be .provided as desired, and that the range 1gates may be either contiguous or overlapping.

1t .is noted .that .the circuits rwhichrespectively :in-

vThe secondY detector, `pulse :amplifier :and -relay switch means indicated -asa block at .54 are conventional `in their circuitry, -and function las an .indicator control or energizing means, applying an energizing voltage through .output lead .56 Vto 4in the :same manner.

an indicator circuit 58 during the time that echo pulses are passed by intermediate frequency amplier 34. Indicator circuit 56 comprises several units corresponding in number to the several ranges provided in the apparatus. Each indicator unit may have a warning light, a warning buzzer, or both, to attract immediate attention of theaircraft pilot whenever hazards in the selected ranges reect echo .pulses .to the equipment. The warning alarm ranges may be readily identiiied without close attention of the operator or pilot by providing brilliant warning lights or" different colors, buzzers or other audible alarms of diiTerent tones, or any other warning indicators of ydistinctive and attention provoking character.

The contiguous or overlapping range gates are inthe illustrated embodiment applied automatically and in repetitive sequence to gate pulse transformer M, and the warning indicator units are correspondingly intermittently connected to output lead 5G. Any suitable electronic or electro-mechanical `means .may be provided for 'this purpose. For example, where but two range `gate circuits and corresponding 'indicator units 5U 4and 62 are provided, as shown, a `double-poledoublethrow switch arrangement `may be used, `in which movablepoints @Il and Si; are-causedto alternately contact corresponding pairs oi stationari7 points. `Theswitchmay 'be actuated by'means-of a small motor,-gear train and cam, here yrepre-- sented by the switch control 'block t8, lcausing movable points'll andf to alternately dwell rst against stationary contacts 'l0 and lf2, respectively, and Athen against stationary contacts 14 and "it, respectively. During the rst `sta-ted dwell condition, indicator Vunit 6B fisconnected to the relayvswitch circuit of unit 54 while af'seriesl 'of relatively long range -gate pulses 'shaped by gate 'forming circuit '5B 'and suitably retarded `by delay line 52 are applied to intermediate 'Erequency ampliiier 3d. 'During the other stated dwell period, indicator unit 62 is connected to the relay switch circuit while aseries of short -range gate pulses are applied to the 'intermediate tirequency'amplier. lDiscrete warnings for both the long. `and short Hranges are thus available without the necessity of manual range selection. '-fIt is tobe understood,`however, that `the apparatus may be designed to have as many or as few ranges as desired, although two ranges as here shown and described-'are 'believed `to be particularly suitable, -and that a .non-automatic, 'manuaL `range selection switch and i'afsingle .warning indicator unit maybe provided for less versatile, 'lighter weight equipment.

When the aircraft bearing the described 'warning apparatus enters an outer hazard zone, th'e longer range indicator vunit {il} -is intermittently energized, causing blinking action-.of the warning light or comparable action of Vany `other form of warning indicator unit utilized. When thehazard distance shortens toless than va pre-set value,'in dicator unit 62 also is intermittently energized In addition to presenting Ahazard warnings over lseveral ranges, the described system 'thus also .functions `to enhance the vlattention demanding character of the warning alarms when overlapping range Vgates are `employed.

The operation of the .equipment maybechecked :at Vany time by .means of the checking .circuit shown in intermediate frequencyampliiierblock .34. A checking voltage source, .suchas albattery it, has .lits `positive terminal by-passed .through a bleeder resistor 80 to ground during the vncrmally closed condition of checker switch 42. By throwing checker switch 42 to an open position, the junction of resistors 40 and 8l! is disconnected from -ground yand the checking voltage is applied to screen grid 36, enabling the intermediate frequency amplifier to pas-s and amplify the small yamplitude search pulses which leak through to the input circuit of the receiver, and causing intiicator units 60 and 62 to be energized in normal fashion. Improper operation or failure of the equipment, generally traceable to defective tubes, is thus readily fand instantaneously detectable under flight conditions.

The hazard distances at which warnings are 74Vgiven' are, of courseia matter of design, being dependent upon the duration and time-position of the range gate pulses relative to corresponding search pulses. The gate pulse circuits may, for example, be designed to provide an initial warning at a distance of 2000 feet, and an 'additional warning at a distance of 500 feet, warning distances which have been found suitable for operation over most terrain. For example, an extensive survey of terrain in the vicinity of airline routes indicates that high mountain peaks are always surrounded by a more or less gradual rise in the terrain such that, for an aircraft ying as much as one thousand feet below the peaks, the 2000 foot warning indicator unit will be energized generally at least several miles in advance, aording ample time for the aircraft to clear it even by a blind climbing maneuver. The 500 foot warning is particularly useful during aircraft let-down operations.

While the invention has here been illustrated in an embodiment which requires the pilot to manually control the aircraft to evade a hazard of which warning is given, the invention may also be employed with an aircraft having automatic 4pilot means for controlling its flight path. Such an autopilot may readily be designed to cause the aircraft to execute Ia hazard-evading maneuver, for example a climb at an initially high land gradualy decreasing rate, in response to the energizing voltage produced at output lead 5-6 when the aircraft is in a hazard zone.

It will be understood that the particular embodiments `of the invention here described have been chosen only by way of example, and that numerous modifications of the system components and changes in their combination and arrangement may be resorted to without departing from the spirit and scope 'of the invention. I therefore contemplate by the appended claims to cover any such modications as fall within the true spirit and scope of the invention.

I claim as my invention:

l. In combination with a pulse-echo system including a search-pulse transmitter, an echo-pulse receiver, pulse radiating and pickup means for said transmitter and receiver, and gating means rendering said echopulse receiver operative during selected intervals to amplify and utilize echopulses, a checking circuit comprising a source of direct-.current potential, and means coupled between said source and said receiver for selectively applying the potentia1 from said source to said receiver to render said echo-pulse receiver continuously operative to amplify and utilize directly received search pulses.

2. In combination with a circuit including a thermionic tube having a control element normallymaintained at a selected potential, said circuit having means applying gating pulses to said control element to change the potential thereon to a given value during gating pulse application, a checking circuit comprising a source of potential, and means coupled between said source and said control element for selectively applying a continuous voltage of said value to said control element.

3. A hazard warning system comprising a transmitter for transmitting periodic search signals; receiving means for receiving echo signals reflected from objects encountered by said Search signals, said receiving means including an output stage and a normally blocked amplier stage; first and second gate signal generating circuits coupled to said transmitter and responsive toV each of'fsaidesearch signals for de- Y' veloping first and second gate signals, respectively, each of said circuits including a delay line of a predetermined time-delay characteris-4 tic; first switching means alternately coupling each of said generating circuits to said ampli` fier stage for a predetermined multiple number of periods of said search signals for applying said gate signals to said amplifier stage to unblock said amplifier stage; first and second indicating means; second switching means alternately coupling each of said indicating means to the output stage of said receiving means for said predetermined multiple number of periods; and switch control means coupled to said first and second switching means for simultaneously actuating said rst and second switching means whereby `said first and second gate generating circuits are coupled to said amplifier stage when said rst and second indicating means are coupled to said output stage, respectively.

4. A hazard warning system comprising a transmitter for transmitting periodic search sig# nals; a receiver for receiving echo signals reflected from objects encountered by said search signals, said receiver including an output stage and a normally blocked amplifier stage; first and second gate -signal generating circuits coupled to said transmitter, each of said circuits being responsive to each of said search signals for developing a gate signal delayed a predetermined time interval after said search signal; first and second indicators; and switching means for alternately applying the gate signals from said gate generating circuits to said amplifier stage for a predetermined multiple number of periods of said search signal to unblock said amplifier stage, and for simultaneously alternately connecting each of said indicators to said output stage for said predetermined multiple number of periods.

5. A hazard warning system comprising a transmitter for transmitting search signals; a receiver for receiving echo signals reiiected from objects encountered by said search signals, said receiver including input and output stages and being normally inoperative to pass signals received at said input stage to said output stage; first and second gate signal developing circuits coupled to said transmitter, said circuits being responsive to each of said search signals for developing gate signals delayed different predetermined time intervals after each search signal, respectively; first and second indicators; and switching means coupled between said gate circuits and said receiver for alternately applying the gate signals from said gate circuits to said receiver to render said receiver operative, said switching means including means coupled between said indicators and said output stage of said :receiver :for .simultaneously alternately connals; a receiver for -receiving `said search signals after reiiection from an object, said receiver including input .and .output stages and being normallyinoperative to pass signals received at said input stage to said output stage; -at least rst and second indicators for providing signals representative of the Ypresence of objects within rst and second predeterminedranges of said transmitter, respectively, at least one point in said second range coinciding with a point in said first range; .at least rst `and second gate signal generating circuits coupled to said transmitter, each `ofsaid circuits being responsive to Asaid Search signals for generating delayed periodic gate signals, the delays introduced by said circuits corresponding, respectively, to the transit times of saidsearch signal toand from an object located at the nearest Vpoint .of said rst and second predetermined ranges; and switching means coupled between said gate circuits and said receiver for .sequentially applying the gate signals .from `said gate `cir-cuits to said receiver .to render said receiver operative, `said switching means including means for simultaneously sequentially connecting Asaid indicators to ,said output stage of said receiver` whereby each indicator is connected to said output .stage during the interval that .the gate signalsfrom its respective gate circuit are applied to .said receiver.

V7. ,A hazardwarning system vas defined in claim 6 wherein the period `during which each of said `gate signalsis applied to said receiver is a multiple or the period of said transmitter.

.8.. In a hazard warning system for indicating the presence of objects within at least Vfirst and second predetermined ranges, said system including `means' for transmitting periodic search signals, a .receiver comprising: an input stage; .an output stage; a normally blocked stage coupled `between said input Vand output stages; ,at least `firstand second indicators, one for each range; atleast rst and second cir-cuits responsive `to the .-search-V :signals for ydeveloping delayed .Per riodiegate signals, the delays introduced .by said first and vsecond circuits corresponding, respectively, to =the transit times of va search signal to and from an object located at the nearest point of said first and second predetermined ranges; a rst switch for sequentially connecting said circuits to said normally blocked stage to apply the gate Isignals to said normally blocked stage to unlock said stage; a second switch for sequentially connecting said indicators to said outputstage; andswitch control means vcoupledto said first and second switches for simultaneously actuating .said switches; the means for transmitting periodic search signals and for developing delayed periodic gatesignals therefrom including means for delaying the beginning `of the second delayed periodic gate signal to a time instant Ano later than the instant of termination of the first periodic gate signal yand terminating 'the vsecond signal after Athe termination ,of therst signaland prior to the transmission of the next search signal.

.MARVIN SKOLLER.

REFERENCES CITED The following references :are of record in the le of this patent:

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